Dr D K Niranjan

OutbreakInvestigation

“A sudden rise in the incidence of a disease”

The occurrence in a community or region of cases of an illness with a frequency clearly in excess of normal expectancy.

What is an “OUTBREAK”?

Endemic infections in hospital Usual or expected frequency of infections in

the hospital (background rate)

Epidemic nosocomial infections in hospital Unusual occurrence of infections clearly in

excess of expected occurrence (background rate)

Isolation of unusual (rare) organism Isolation of organism with different anti-

microbial susceptibility, or molecular typing

Common source epidemics Single source or point source Continuous or Multiple exposure

Propagated epidemics Person to person spread

Types of outbreaks

Outbreak in Hospital/ Health facility

Outbreak in Community

Outbreak in community may have origin in a hospital

Outbreak in community may trigger outbreak in hospital

We take almost similar steps to investigate community and hospital outbreaks

Infection control programme in hospital may not only prevent outbreak in hospital, but in community also

Places of Outbreak

Prevent additional cases in the current outbreak

Prevent future outbreaksLearn about a new diseaseLearn something new about an old diseaseReassure the publicMinimize economic and social disruptionTeach epidemiology

Why the outbreaks need to be investigated?

MagnitudeCharacterization of cases by time, person and

placeRisk factorsSource of infection, mode of transmissionControl of outbreakPrevent recurrenceDocument the outbreak – lessons learnt

Objectives of outbreak investigations

EpidemiologistClinician/paediatrician/ neonatologistMicrobiologistMember of Hospital Infection Control

CommitteeStaff from affected unit/wardOthers depending on the need

Outbreak Investigation Team

Confirm the diagnosis Confirm the existence of an outbreak Define at-risk population and characterize the

cases by time, person and place (Case definition; case ascertainment – identify and count cases; line list of cases; epidemic curve)

Review of literature about outbreaks/isolates Formulate hypothesis about genesis of outbreak

(source and route of infection) Make further investigations to confirm/refute the

hypothesis (case control studies, culture surveys) Control the outbreak Prepare and disseminate the report

(documentation)

Steps of outbreak investigations

Case definition changed Introduction of new laboratory tests Frequency of testing of patients changed Introduction of a new medical or surgical

procedure New areas or population included under

the surveillance

Factors other than outbreak may explain increase in infection rates

Confirm outbreak – Confirm diagnoses – Case definition – Case line listing started – Case finding – Case interviews – Complete line listing – Case descriptive epidemiology – Establish baseline occurrence of cases – Rule out alternative explanations (chance,

bias, ...) Generate preliminary causal hypotheses

1. Case investigation

Standard set of criteria for deciding if a person should be classified as suffering from the disease under investigation.

Clinical criteria, restrictions of time, place, person characteristics

Specific inclusion and exclusion criteria Simple, practical, objectiveSuspect, probable, confirmed

Case definition may be more sensitive initially

Case definition should be more specific when sufficient information is available

Case definition

Identification No.AgeSexDate of admissionCause of admission Intervention/surgery/procedure done, device used, if anyDate of undertaking intervention/surgery/procedure Place where intervention/surgery/procedure undertakenDate of onset of outbreak associated clinical featuresOutbreak associated clinical features Lab investigationsResult of lab investigationsDiagnosis (Nosocomial infection)Outcome: Still ill, recovered, died, other (specify)Other relevant variablesComments

Line List of Cases

Examples of epidemic curves 0

5

10

15

20

25

1 3 5 7 9 11 13 15 17 19

0

5

10

15

20

0

5

10

15

20

Multiple curves

Point source

Continuous source

Compare hypotheses with facts

• Who is at risk of becoming ill?• What is the disease causing the

outbreak? • What is the source and the vehicle?• What is the mode of transmission?

Develop hypotheses

Systematically review known causal factors (Transmission mechanisms and dynamics)

Prioritize likely causes to guide controlmeasures (Step 3)Generate testable hypotheses to conduct

analytic study (Step 4) if cause remains unknown or control measure not working

2. Cause investigation

Epidemiologic/clinical investigation

Environmental investigation

Laboratory investigation

Veterinary or vector borne investigation

Forensics/Law enforcement investigation

3. Control measures (do early)

Implement control measures

May occur at any time during the outbreak!!

Prevent recurrence

Control the source of infection

Interrupt transmission

Modify host response

Control measures related to source of infectionIdentify and remove the source of infectionIsolation of casesQuarantine of healthy contacts of infectious

diseaseInterrupt transmissionProtect susceptible host

ImmunizationChemoprophylaxis

Non specific measuresSurveillance programme for detection/control of

infectionsRisk communication (IEC)Research

Control of Outbreaks

Prepare study protocol1. Primary question(s)2. Significance3. Design4. Subjects5. Variables6. Statistical issues● Conduct study● Analyze data● Interpret findings

4. Conduct analytic study

Epidemiologic inference Validity (internal and external) Threats to validity

Causal inference– Causal criteria– Causal models

5. Conclusions (inference)

Inferences in epidemiology

Detect outbreaksDetect public health threatsDetect infectious cases (case finding)Monitor trends in a target populationMonitor exposed individuals for symptomsMonitor treated individuals for complicationsDirect public health interventionsEvaluate public health interventionsGenerate hypotheses for further evaluation

6. Continue surveillance

Communicate preliminary assessments and recommendations (letter, memo)

Prepare interim/final reportsPrepare manuscript (optional)Risk communication strategy (what to say)Media communication strategy (how to say it)

7. Communicate findings

Every outbreak in the hospitals is an

opportunity to improve infection control

programme. Lessons learnt should be used to prevent future outbreaks

Assign a spokesperson who has the authority, is knowledgeable and respected by community, health professionals and media

Give clear, accurate and timely information. Avoid technical terms, if possible. Update information regularly.

Forward 3 positive points against one negative point.

Do not allow media to control the entire dialogue

Be frank about your efforts and the challenges

Tackling the media

Chronology of events - How was the outbreak suspected?

Methodology adopted for investigation Outbreak investigation Team Case definition Case ascertainment Lab investigations

Epidemiological observations Characterization of cases/deaths by time, person and place

Results of laboratory investigations Analysis and interpretation of data collected and

compiled Further investigations undertaken Conclusion about source and route of infection Interventions made/recommended Dissemination of report including executive summary to

all stakeholders

Outbreak Investigation Report

Viral hepatitis B outbreaks occurred in hospitals in 1980s and 90s

In 1997, NICD investigated 3 community outbreaks of viral hepatitis BMehasana district in GujaratSirsa district in HaryanaSri Ganganagar in Rajasthan

Inadequately sterilized needles and syringes resulted in these outbreaks

Inadequate sterilization still causes many infectious diseases outbreaks in hospitals

Viral hepatitis B outbreaks in 1997

Source: WHO 1998; 76:93-98; Epidemiol Infect 2000;125:367-375

ESI Hospital Colony, Madurai had an explosive outbreak of chikungunya in September 2009

Chikungunya cases were admitted to the ESI HospitalThere was heavy breeding of Aedes mosquitoes in the

campusInfection was transmitted to other cases and hospital

staff9 of 11 doctors and 34 of 37 nurses who worked in

the hospital or stayed in the campus were affected during the outbreak

Most of other residents of the hospital colony were also affected

Hospital transmission of dengue and chikungunya has been observed in other cities also in the past

Outbreak of Chikungunya in ESI Hospital Colony, Madurai, 2009

A patient admitted in a hospital probably started the outbreak

Infection spread to other patients, visitors and health acre workers

66 probable cases, 45 diedMany including health care workers got

infection in the hospitalNo exposure of cases to animalsHuman to human transmission of Nipah/

Hendra virus was suspected

Outbreak of Nipah/Hendra virus in Siliguri, 2001

Source: IJMR 2006;123: 553-560

Thank You